Next generation broadband internet access networks are based on fiber to the home (FTTH) architectures, which overcome the bandwidth limitations of copper-based transmission technologies. Most FTTH deployments either use dedicated fibers for each customer in a star topology, or passive optical networks (PON), which use a tree-shaped topology with a single feeder fiber trunk, optical splitters, and dedicated drop fibers as branches of the tree. For a PON, subscriber access to the endpoints of the shared medium is controlled by a TDMA-based mechanism.
The tree-shaped topology of PONs has disadvantages in terms of shared bandwidth, security and upgradability. Star topologies require significantly more fibers to be terminated at a central office. An alternative to the above methods is to deploy a dense wavelength division multiplexing (DWDM) PON. A DWDM PON uses per-subscriber wavelengths to share a feeder fiber and employs arrayed waveguide grating (AWG) to route individual wavelengths to individual endpoints on both the subscriber-side and central office-side. Thus, a DWDM PON combines the best of both worlds: scalability, upgradability and security of star architectures, and the fiber sharing of tree architectures.
For a DWDM PON application, one challenge is to provide a wavelength division multiplexing (WDM) transmitter for each end user to allow upstream communication from a subscriber to the central office. An efficient way to accomplish this is to use spectral slicing with an injection locked Fabry-Perot (FP) laser or an injection locked reflective semiconductor optical amplifier (RSOA). In this architecture, a broadband light source (BLS), a laser array, or similar structure is used to seed a Fabry-Perot laser or RSOA in each optical network unit (ONU). The BLS spectrum propagating toward the subscriber's remote node is sliced by an AWG in the remote node. The sliced continuous wave seed light is used to “injection lock” the FP/RSOA laser transmitter within the subscriber's ONU. The same approach is used for the downstream signal: at the OLT/central office, the FP/RSOA transmitter is injection-locked by a BLS propagating towards the central office. Thus, the upstream/downstream signal depends on the operability of the seeding source (i.e., the BLS).
Overview
Embodiments described in this disclosure provide techniques for allowing a broadband service provider to maintain continuity of service in the event that a broadband light source fails in a passive optical network which uses injection-locked transmitters.
One embodiment includes a system configured to maintain continuity of service to a passive optical network (PON). The system may generally include an active broadband light source (BLS) providing service to a dense wavelength division multiplexing (DWDM) PON, a standby broadband light source; and a monitoring device. The monitoring device may be configured to detect a failure of the active BLS providing service to the DWDM PON, disconnect the active broadband light source from the DWDM PON, and connect the standby broadband light source to the DWDM PON. Once connected, the standby broadband light source provides service to the DWDM PON. In a particular embodiment, the system includes a plurality of active broadband light source (BLSs) each providing service to a respective DWDM PON. In such a case, the standby BLS may be connected to any one of the respective DWDM PONs upon detecting a failure of a given active BLS.